yeah you can do that. Look at big shows, where everything is run through teh house system. It all depends on the quality and power of the PA youre going to use. (a 60 watt rogue with 10" cabs will not handle bass well) but larger systems, with subwoofers, and multiple good sized poweramps can take the place of an amp entirely. bass can be run direct into the PA through a DI box. you could do that with guitar, but most guitarist dont want to lose the tone of their amp and effects. In my band back home we have two guitar players, two sometimes three vocalists, and of course bass. Everything, including bass and drums, is miced or fed directly into the mixer via the direct out in back of the amps.

We've been doing it at rehearsal to avoid lugging our stage amps. It works bitchen. We run 5 mics, bass, lead, and two rythym guitars through a Mackie 1402 VLZ Pro and a QSC power amp into our EV 12-inch floor monitors. We don't use the PA speakers at rehearsal. I run my bass through a SABDDI and Boss CE-3 Chorus, and the guitar players run through various layers of effects and multi-effects. The electric rythym guitar uses a Boss Stereo Chorus, TU-2 Tuner and SansAmp GT-2. The acoustic guitarist uses my SansAmp Acoustic DI. The Lead guitarist uses a DOD Disto fo some kind and a DOD multi-effect.

We can get an excellent mix out of this ... so much so, that we're thinking of doing at a show sometime, only run the big JBL PA speakers. It might be interesting.